Sheet steel coated with an aluminum alloy

ABSTRACT

A STEEL SHEET, COATED WITH AN ALLOY OF ALUMINUM AND CHROMIUM OR TITANIUM, FOR USE AS A CONTAINER FOR BEER. THE COATING COMPOSITION IS SELECTED SO THAT ANY GALVANIC CURRENT BETWEEN THE STEEL AND THE COATING IS MINIMAL.

Mud! 19 B. c. SEILER 3,567,409

SHEET STEEL COATED WITH AN ALUMINUM ALLOY Filed Nov. 15. 1967 '/o 20 a0 40 0 60 70 80 90/00 A Cf/ROM/UM CURRENTOad) TNVENTOR 0 /0 40 6'0 /00 A. r/m/wuM flemard C. Sei/er United States Patent O 3,567,409 SHEET STEEL COATED WITH AN ALUMINUM ALLOY Bernard C. Seiler, Bethlehem, Pa, assignor to Bethlehem Steel Corporation Filed Nov. 15, 1967, Ser. No. 684,901 Int. Cl. B32b 15/18,.15/20 US. Cl. 29-1962 5 Claims ABSTRACT OF THE DISCLOSURE A steel sheet, coated with an alloy of aluminum and chromium or titanium, for use as a container for beer. The coating composition is selected so that any galvanic current between the steel and the coating is minimal.

BACKGROUND OF THE INVENTION This invention relates to ferrous metal articles having a metallic coating thereon, and more particularly to sheet steel coated with an alloy of aluminum and chromium or titanium.

Steel which is to be used as containers for beer must be coated to protect the steel from chemical corrosion by the beer. When the coating is metallic, a break in the coating results in a galvanic current between the coating and the steel, the beer acting as an electrolyte. Depending upon the electrochemical potential of the coating, either the coating or the steel will dissolve in the electrolyte as a result of the galvanic current, the rate at which metal goes into solution being dependent upon the magnitude of the galvanic current.

It has been found that very small amounts of iron in beer, e.g., 0.5 part per million, can detract substantially from the desirable properties thereof, e.g., taste and odor, while relatively much larger amounts of other metals, e.g., aluminum, can be tolerated without detracting from these properties.

In the past, many beer containers were coated with tin. However, small amounts of tin can also substantially detract from the desirable properties of beer and, in addition, the chemical corrosion resistance of tin is such that it is generally necessary to apply two coats of enamel to the tin coating to prevent chemical corrosion thereof by the beer. Also, the worlds sources of tin are very erratic, and the price of tin is relatively high.

It is an object of this invention to provide a coated ferrous base, to be used as a container for beer, in which the electrochemical potential of the coating is approximately equal to the electrochemical potential of the ferrous base.

It is a further object to provide a coated ferrous base, the coating having a chemical corrosion resistance to beer which is superior to that of tin.

SUMMARY OF THE INVENTION I have discovered that the foregoing objects can be obtained by providing a coated ferrous base, the coating consisting essentially of 15 to 50 weight percent of one member of the group consisting of chromium and titanium, balance aluminum. Such a coating, when exposed to beer, rapidly polarizes to substantially the same electrochemical potential as the ferrous base and, in addition, has a chemical corrosion resistance to beer which is much greater than that of tin.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the corrosion currents in beer between a sheet steel base and a coating material consisting of aluminum-chromium alloys.

Patented Mar. 2, 1971 FIG. 2 is similar to FIG. 1, except that the coating material consists of aluminum-titanium alloys.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show the variation in corrosion current, 1n microamperes, between an electrode of sheet steel and an electrode comprising a glass panel upon which a coating material has been deposited, as the composition of the coating material is varied. The electrodes were immersed in beer, at 78 F., and current readings were taken after 17 hours, at which time the current had reached a fairly steady state condition.

The abscissa is in terms of percentage composition, While the ordinate is in terms of current between the electrodes. Positive currents indicate that the coating material is anodic, while negative currents indicate that the steel is anodic.

The metal coatings, which may be deposited on the glass panels by vapor vacuum deposition, have little or no crystal structure, and may therefore be considered as being solid solutions. As used herein, the term alloy is meant to include such solid solutions.

As is shown in FIGS. 1 and 2, there is a positive corrosion current of about 5 microamperes between a aluminum coating and sheet steel, while there is a negative current, between both 100% chromium and 100% titanium, and sheet steel. As the percentage of aluminum in the coating decreases, the current also decreases, and passes through zero at about 55 to 60% aluminum (35 to 40% chromium or titanium). Within the broad range of about 15 to 50% chromium, balance aluminum, the current is less than about 1.5 microamperes, While for coatings containing titanium instead of chromium within this range the current varies from about +1.0 to -O.5 microampere.

Coating alloys within the above broad range, viz, 15 to 50% chromium or titanium, balance aluminum, and a panel of tin were immersed in beer at 78 F. for a three week period to determine the chemical corrosion resistance thereof. At the end of this period, the tin was completely dissolved in the beer, while the aluminum-chromium and aluminum-titanium coatings were not noticeably attacked.

In view of the foregoing, it can be seen that steel cans coated with aluminum alloys within the above broad ranges have excellent resistance to both chemical and electrochemical corrosion. This resistance may prove sufficiently good so that only a single coat of enamel need be applied to the alloy coating. However, even if two coats of enamel are required, any damage to the enamel coating will result in considerably less corrosion of the protective metal coating than if the steel had been coated with tin.

Preferably, the composition of the coating alloy is selected so that the coating is always anodic with respect to the sheet steel base. In the case of the aluminumchromium alloys, this composition is 20 to 40% chromium, balance aluminum, while for the aluminum-titanium alloys the composition is 20 to 35% titanium, balance aluminum. In the former case, the corrosion current varies from about 0 to 1.5 microamperes, while in the latter case said current varies from about 0 to 0.8 microampere.

As a result of these very low corosion currents, as well as the fact that iron will not dissolve electrochemically in the beer, steel cans coated with alloys within these narrow ranges may not need to have any enamel applied to the alloy coating. Here again, if an enamel coating is found necessary, any damage to the enamel coating will result in considerably less corrosion of the pro- Mn P S Cu, Sn,

percent percent percent percent percent percent Broad. 03-. 60 003-. 020 010-. 050 010. 200 001-. 050 Narrow- 04-. 12 20-. 50 005-. 015 015-. 030 0010-. 060 001-. 030

Balance iron.

The steels used to plot the corrosion current data shown in FIGS. 1 and 2 had the following compositions:

0 Mn P S Cu Sn Balance.

Percent- 0. 068 0. 22 0. 008 0. 024 0. 023 0. 004 Iron. Percent- 0. 085 31 0. 008 0. 025 0. 030 0. 005 Iron.

The alloy coatings may be applied to the sheet steel by means of standard vapor vacuum deposition techniques. Such techniques are described, for example, in Vacuum Deposition of Thin Films, by L. Holland, 1961, published by John Wiley & Sons, Inc, and Advances and Future of Electron Beam Processes, by H. R. Smith and C. dA. Hunt, Second International Conference on Electron and Ion Beam Science and Technology, Apr. 17-20, 1966, New York.

It should be understood, in this specification, that wherever percentages are referred to, such percentages are by weight.

I claim:

1. A coated sheet steel, the coating consisting essentially of 15 to 50 weight percent of one member of the group consisting of chromium and titanium, balance aluminum.

2. An article as recited in claim 1, in which said steel consists essentially of carbon 0.03 to 015 Weight percent, manganese 0.20 to 0.60 weight percent, phosphorus 0.003 to 0.020 weight percent, sulfur 0.010 to 0.050 weight percent, copper 0.010 to 0.200 Weight percent, tin 0.001 to .050 weight percent, balance iron.

3. An article as recited in claim 2, in which said steel consists essentially of carbon 0.04 to 0.12 weight percent, manganese 0.25 to 0.50 weight percent, phosphorus 0.005 to 0.015 Weight percent, sulfur 0.015 to 0.030 weight percent, copper 0.010 to 0.060 weight percent, tin 0.001 to 0.030 weight percent, balance iron.

4. An article as recited in claim 1, in which said coating consists essentially of 2 to Weight percent chromium, balance aluminum.

5. An article as recited in claim 1, in which said coatconsists essentially 0f 20 to 40 weight percent chrotanium, balance aluminum.

References Cited UNITED STATES PATENTS 2,490,978 12/1949 Osterheld 29-196.2X 2,917,818 12/1959 Thompson 29196.2 2,932,585 4/1960 Hubbell et al. 29-197X 3,197,861 8/1965 Brick 29196.2X 3,337,427 8/1967 Whitfield et al 29197X 3,365,327 1/1968 Puyear et a1. 29197X 3,392,014 7/1968 Yonezaki et al. 3,415.67). 12/1968 Levinstein et al. 29196.2X

L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner US. Cl. X.R. 29-196.6, 197

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,567,409 Dated March 2, 1971 Inve t r-( Bernard C Seiler It is certified that error appears in the above-identified paten and that said Letters Patent are hereby corrected as shown below:

Column 3, line 9 under Cu per cent "00l0- .060" should read .010- .060 Column 4 line 14 "2 to 40 should read 20 to 40 line 1 7 "20 to 40 weight percent chrotanium" should read 20 to 35 weight percent titanium Signed and sealed this 20th day of July 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, JR Attesting Officer Commissioner of Patents FORM PC4050 [10-69] s A I H A 

